Platform Requirements
Java version
uPortal 3 requires JDK 1.5. It may work without modification on JDK 1.6 when it is released, but JDK 1.5 is the target platform. Since uPortal 3 takes advantage of Generics and other JDK 1.5 innovations, it is likely a daunting project to back-port it to run on JDK 1.4.
Tomcat
uPortal 3 runs in Tomcat 5.5.x . It can probably be made to run in a Tomcat 5.0 and in other servlet containers. However, Tomcat 5.5 is the opensource container of choice.
Hardware
The hardware requirements for various sized uPortal 3 deployments are not yet known. See the listing of current uPortal 2.5.x deployers and the information they have shared about deployment environment for a rough idea.